JPH04141983A - Thin film electroluminescent element - Google Patents

Abstract

PURPOSE:To improve the dielectric strength by providing a transparent electrode consisting of ITO formed on a smooth surface of a surface irregularity of not more than 700Angstrom , and forming a dielectric layer on it. CONSTITUTION:A transparent electrode 2, a first dielectric layer 3, a light emission layer 4, a second dielectric layer 5, and a back electrode 6 are formed on a substrate 1, where the transparent electrode 2 is formed setting a surface irregularity of less than 700Angstrom by ITO. By thus forming the dielectric layer 3 on the transparent electrode 2 having a smooth surface, partial reduction of a film thickness or an abnormal growth can be reduced. A thin film electroluminescent element of a good dielectric strength can thus be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film EL device that is attracting attention as a flat panel display, and particularly to a thin film EL device that has excellent dielectric strength.

[Conventional technology]

Thin-film EL devices have been attracting attention in recent years because they can be used to create flat, thin, and large-area display panels, and can be used for a wide variety of purposes, from numerical displays to graphic displays and image displays.

The basic structure of such a thin film EL element is that a transparent first electrode (transparent electrode) made of a tin oxide layer or the like is placed on a glass substrate, and a T
A first dielectric layer (first insulating layer) made of a dielectric such as A205, and ZnS.

A light-emitting layer in which a base material such as CaS or SrS is doped with a luminescent center impurity such as Mn, Ce, or Eu, a second dielectric layer (second insulating layer), and a second electrode (back electrode) consisting of an aluminum layer or the like. It has a double-insulated structure in which these are sequentially laminated.

Then, when a voltage is applied between the transparent electrode and the back electrode, the electric field induced in the light-emitting layer pulls out and accelerates the electrons trapped in the interface level, obtaining sufficient energy and causing these electrons to It collides with and excites the orbital electrons of the luminescent center, and emits light when the excited luminescent center returns to its ground state.

[Problem to be solved by the invention]

When a thin film EL element is formed using ITO, which has a highly uneven surface, as the transparent electrode, the dielectric layer (insulating layer) formed thereon by a sputtering method may have a thin effective film thickness or abnormal growth. This increases the number of parts that can cause damage, resulting in a lower dielectric breakdown voltage, making it more likely to cause dielectric breakdown.

Therefore, an object of the present invention is to solve the problems of the prior art as described above and to provide a thin film EL element with good dielectric strength.

[Means and effects for solving the problem] According to the present invention, in order to achieve the above object, a transparent electrode is formed using ITO so that the surface irregularity is 700 Å or less. Here, 700 Å or less means that the difference in height between convex and concave portions (or between concave and convex portions) of the surface unevenness and between the convex portions is 700 Å or less.

As shown in FIG. 2, I formed on the glass substrate (1)
When the surface of the transparent electrode (2) made of TO is extremely uneven, when the dielectric layer (3) is formed on the transparent electrode (2), as described above, the effective film thickness becomes thin (A). The number of parts (B) that cause abnormal growth increases. Even if an EL element is manufactured in such a state, the element will be susceptible to dielectric breakdown.

However, when a dielectric layer is formed on a transparent electrode with a smooth surface as in the present invention, it is less likely that the film will become thinner locally or that abnormal growth will occur. Therefore,
If an EL element is manufactured in such a state, dielectric breakdown will be less likely to occur.

〔Example〕

The present invention will be specifically described below with reference to Examples.

Example 1 As shown in FIG. 1, ITO was deposited as a transparent electrode (2) by sputtering on a glass substrate (1) by 1,500 people.

The surface condition of this ITO was extremely smooth with about 200 convex to 5 pitches. Next, after patterning by photolithography, a first dielectric layer (3) of 1000 T:SiON was formed by sputtering, and then a light emitting layer (4) of ZnS:M was formed.
n of 5000 people, MSD method (multiple evaporation method: Each constituent element of the luminescent layer base material (ZnS) and the luminescent center impurity (M n ) are placed in separate crucibles in a vacuum chamber, and the temperature of each is controlled independently. For details on the method of vapor deposition by heating while
4)). Next, 5iON was formed as a second dielectric layer (5) by 1000 people using a sputtering method, AM was deposited thereon by 3000 people using an electron beam evaporation method, and then Cu was deposited by 3000 people using an electron beam evaporation method.
Next, patterning was performed using photolithography to form a back electrode (6).

In this way, when a thin film EL element was formed using ITO with a smooth surface, an element without large dark spots (50 μm or more in diameter) or disconnections could be obtained.

Example 2 A thin film EL device was fabricated in the same manner as in Example 1, except that an ITO film with a smooth surface with a convex-to-convex spacing of about 300 to 400 was formed by electron beam evaporation. We were able to obtain an element with no wire breakage or disconnection.

For comparison, the convex-convex spacing was approximately 80 by electron beam evaporation.
A thin-film EL device was fabricated in the same manner as in Example 1 above, except that an ITO film with a rough surface of about 0 to 1000 nm was formed.The resulting device had poor dielectric strength, large dark spots, and disconnections. It had

〔Effect of the invention〕

As described above, the thin film EL element of the present invention has a transparent electrode made of ITO formed on a smooth surface with surface irregularities of 700 Å or less, and has a dielectric layer formed thereon. The thickness of the body layer is uniform, there is little chance of partial thinning or abnormal growth, and the resulting dielectric strength is excellent.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the thin film EL element of the present invention, and FIG. 2 is a schematic diagram showing a state in which a dielectric layer is formed on a transparent electrode with a highly uneven surface. 1 is a glass substrate, 2 is a transparent electrode (ITO), 3 and 5 are dielectric layers (S 1ON), 4 is a light emitting layer (ZnS:Mn)
, 6 is the back electrode.

Claims (1)

[Claims] A thin film in which a transparent electrode, a first dielectric layer, a light emitting layer, a second dielectric layer, and a back electrode are formed on a substrate, and which emits EL light by applying a voltage between the transparent electrode and the back electrode. A thin film EL device, characterized in that the transparent electrode is ITO formed on a smooth surface with surface irregularities of 700 Å or less.